Does feeding birds in winter make them dependent on humans?
Some nature lovers worry that birds will become accustomed to free handouts from backyard bird-feeding stations and lose their natural ability to forage. Research at the University of Wisconsin contradicts this theory. Researchers discovered that when birds add a human-provided source of food to their diet, they do so without eliminating sources in nature, such as insects, seeds, and fruits. Your bird feeder simply becomes one more stop in their regular feeding pattern.
The same study showed that feeders improve the winter survival rates of birds, especially in late winter or after a heavy snowfall, when natural food sources diminish. When the researchers removed the feeders, the birds showed no loss of foraging skills.
In addition to setting out a well-stocked feeding station, there are other ways of assisting birds in winter. For example, you can landscape your yard with native plants that offer food and shelter. And birds welcome a source of water in all seasons. This article details a few other wintertime strategies for creating a bird-friendly yard. —Doug Hall
How is it that some plants survive temperatures below zero, when my tomatoes turn to mush at the first hint of frost?
Plants that live in cold climates have developed the ability to withstand below-freezing temperatures without damage. When you consider that each living cell is filled mostly with water, this is an amazing feat.
Plants such as your tomatoes—as well as other tender annuals and tropical plants—can’t survive freezing. When the water in their cells turns to ice crystals, cell walls rupture and the tissues die.
Hardy evergreens, on the other hand, fortify their cells with sugars and other dissolved substances as winter approaches, turning water into an “antifreeze” of sorts. The foliage of both broadleaf and needle evergreens usually has a waxy layer that offers extra protection. Hardy deciduous trees and shrubs can also freeze-proof the sap in their woody tissues.
You’ve probably noticed an interesting side effect of the autumn buildup of sugars in plant cells. After the first light frosts of fall, cool-weather vegetables like broccoli, kale, and Brussels sprouts begin to taste sweeter—evidence that the plants are bracing for cold.
But even antifreeze has its limits, and that’s where the USDA Plant Hardiness Zones come in. These hardiness ratings give gardeners a good idea of just how much winter cold each species can tolerate. —Doug Hall
Can I use my Christmas tree for mulch?
The boughs of fir, pine, spruce, and other evergreen trees are a good insulator for dormant perennials. Unlike some winter mulches, like unshredded leaves, they don’t pack down into a solid, oxygen-excluding layer. And when spring comes, they’re easy to rake aside.
Discarded Christmas trees appear curbside at an ideal time for adding winter mulch in my Zone 6 garden. By late December, the ground has chilled (if not frozen an inch or two deep) and plants are dormant. Hopefully, any field mice in the neighborhood have settled down elsewhere for the winter and won’t find habitat in my mulch. I scavenge the neighborhood before trash day, bringing home five or six trees to cut apart.
It’s quick and easy: Just snip the tree’s branches off with loppers. Place the boughs over the crowns of perennials or around roses.
The purpose of winter mulch is not to keep plants warm but to keep them consistently cold and dormant. Unmulched plants are exposed to temperature fluctuations, alternating between overnight freezing and daytime thawing when the sun hits the soil. Some plants shrug off these repeated temperature changes, but anything of marginal hardiness will appreciate the extra protection it gets from a layer of evergreen boughs. —Doug Hall
I will be moving in January and I’m sad at the thought of leaving all my beautiful perennials behind. The ground here in Zone 5 will be too frozen to dig in January, but I can’t return next spring to dig them either. Can I put them in pots this fall?
That’s a great plan. You can dig divisions of your favorite perennials in late summer or early fall and pot them in plastic nursery pots. If you are paying a moving company to transport your possessions, keep in mind that you’ll probably be charged by weight; smaller divisions in small, lightweight pots will save moving fees. Some movers refuse to transport plants at all, so check the fine print of your contract.
Getting the plants through a cold winter in pots will be the tricky part. Leave the potted perennials outdoors as the weather cools in fall, allowing them to gradually go dormant. If you anticipate the soil may freeze before your moving date, cluster the pots together outdoors and insulate over and around them with loose mulch such as straw or evergreen boughs, then cover them with a tarp. Or keep the pots in an unheated garage. Once the soil in the pots freezes, it’s best that it stay frozen and not alternate between frozen and thawed.
After the pots have arrived at your new home, continue to keep the plants chilled and dormant until spring planting season. —Doug Hall